Conventionally, a vehicle has a hydraulic control system which includes a hydraulic unit for regulating a wheel cylinder pressure by actuating a solenoid valve, a pump motor which serves as an actuator for regulating a hydraulic pressure, an electronic control system which controls the hydraulic unit and drives the pump motor, and the like. In order to reduce the size of the hydraulic control system, the hydraulic unit, the pump motor and the electronic control system are integrated into a module.
In a hydraulic control system like this, it is particularly important that a solenoid portion of the solenoid valve is not exposed to water and dust in order to prevent a breakdown or corrosion. To achieve this objective, the solenoid portion could be disposed in an air-tight chamber. However, when an in-vehicle air-tight chamber is subjected to a severe temperature change, water vapor is likely to enter the air-tight chamber and dew is likely to condense therein.
In order to address this problem, a solenoid valve housing chamber for housing a solenoid portion of the solenoid valve usually includes an air vent. The air vent allows water to enter a solenoid valve housing chamber and facilitates draining of the water that has entered (for example, as disclosed in Japanese Patent Application Laid-Open 2001-124005).
There are some cases where water entry into the solenoid valve housing chamber having an air vent like this occurs because the air vent is immersed in water, whereby water pressure is applied to the air vent. Another reason for water entry is as follows. When the temperature of the solenoid valve housing chamber installed in an engine room is relatively high in accordance with an actuation state of the solenoid valve, and if a case in which the solenoid valve housing chamber gets wet due to water on a road surface being splashed thereof, the temperature in the solenoid valve housing chamber drops. When the pressure in the solenoid valve housing chamber becomes negative due to a sudden temperature change like this, water which has splashed onto the case in the vicinity of the air vent is sucked into the solenoid housing chamber by the negative pressure, whereby water enters the solenoid valve housing chamber.
In the above described conventional art, an air passage that is repeatedly bonded to form a labyrinth structure formed is used to communicate the solenoid valve housing chamber with the outside, via the housing and a pump case. However, manufacturing of the air passage requires an additional processing for the housing and a structural change in a motor portion, whereby cost is increased.